Conventional expansion joints employ stuffing boxes of the type which have inner and outer telescopically arranged members forming an annular chamber therebetween for receiving a semi-plastic packing material. When the packing material is packed into this chamber under pressure, a reliable seal is established. The seal is maintained even when the outer and inner telescopically arranged members move relative to one another. For example, prior known designs of expansion joints which utilize stuffing boxes are disclosed in U.S. Pat. Nos. 1,151,614; 1,947,072; 1,960,041; 1,989,644; 1,953,493; 2,319,543; 2,714,024; 3,258,271 and 3,876,213.
The reliability of a packed expansion joint is dependent upon the effectiveness of the seal established between the stuffing box packing and the adjacent surface of the adjacent member which slides relative to the stuffing box. Said surface is ordinarily the exterior surface of the interior telescopic member and usually comprises a highly polished, hard, smooth coating material such as chrome. It is essential to maintain this surface in an unscored, unworn condition in order to assure a proper seal.
As far as is known, all prior expansion joints have had the deficiencies that the exterior sleeve, in which the stuffing box cavity is formed, tends to score or otherwise wear the smooth exterior surface of the interior telescopic member when the two cylindrical members become misaligned. Such scoring or wear resulting from metal to metal sliding contact rapidly leads to failure of the seal established by the stuffing box. Misalignment of the telescopic inner and outer members may be expected to occur as a result of maladjustment or failure of a pipe support which causes the axes of the members to be skewed relative to one another or as a result of a packing operation which asymmetrically loads up one side of the stuffing box thereby causing the inner and outer telescopic members to be shifted laterally relative to one another.
Expansion joints of the above discussed type are specifically provided to absorb thermal expansion in a pipeline which carries fluids of fluxuating temperatures. Pipeline systems lacking expansion joints or having jammed expansion joints caused by corrosion of the joint or misalignment of the joint can develop tremendous stresses. The unrelieved stresses of such a system may result in damage to or destruction of overstressed pipe hangers and/or components of the system. Thus is posed the technical problem of providing an expansion joint which avoids scoring or wear of the highly polished slip surface even though the inner and outer members become misaligned.